Fate of 14C-ethyl prothiofos insecticide in canola seeds and oils

Abstract

Canola plants were treated with 14C- prohiofos under conditions simulating local agricultural practices. 14C-residues in seeds were determined at different time intervals. At harvest time about 32 % of 14C-activity was associated with oil. The methanol soluble 14C-residues accounted for 12 % of the total seed residues after further seeds extraction, while the cake contained about 49 % of the total residues. About 69 % of the 14C-activity in the crude oil could be eliminated by simulated commercial processes locally used for oil refining. Chromatographic analysis of crude and refined oil revealed the presence of the parent compound together with three metabolites which were identified as prothiofos oxon, O-ethyl phosphorothioate and O-ethyl S-propyl phosphorothioate, besides one unknown compound. While methanol extract revealed the presence of despropylthio prothiofos and O-ethyl phosphoric acid as free metabolites acid hydrolysis of the conjugated metabolites in the methanol extract yielded 2, 4-dichlorophenole which was detected by color. When rats were fed the extracted cake for 72 hours, the bound residues were found to be bioavailable. The main excretion route was via the expired air (42 %), while the 14C-residues excreted in urine and feces were 30 % and 11 %, respectively. The radioactivity detected among various organs accounted to 7.5 %.Chromatographic analysis of urine indicated the presence of prothiofos oxon, O-ethyl phosphoric acid and 2, 4-dichlorophenole as main degradation products of prothiofos in free and conjugated form.